The proposed work is a part of a general laboratory effort to evaluate factors that regulate the growth and differentiation of hematopoietic cells. During the coming year humoral factors regulating the growth of pluripotential stem cells in vivo and in vitro will be studied as will the effect of anemia in influencing the tissue localization of this cell population. The roles of alterations in acid-base balance and in blood levels of carbon dioxide in regulating the production of erythropoietin will be further evaluated.